1. Field of the Invention
This invention generally relates to lifting devices and more particularly to devices employed in removing and installing rotating conveyor rolls in a continuously operating conveying system.
2. Description of the Prior Art
In the production of glass, it is customary to produce a continuous ribbon of glass from a molten mass and pass this plastic ribbon through an annealing lehr which operates continuously with a melting furnace producing the molten mass of glass. It is well known that in passing the continuous glass ribbon through the lehr, that it is conveyed on rolls that are commonly driven from a continuously operating drive train. Customarily, each roll in the conveying system is driven by a worm gear connected to a mechanical line shaft extending the length of the lehr. Since the lehr must be operated continuously in producing the glass ribbon, the replacement of defective conveyor rolls, for example those requiring grinding, is a problem as they are heavy and of large size and must be replaced while the lehr is operating.
Heretofore, a defective conveyor roll was replaced by first inserting a bar into the driven open end of the roll, which is normally hollow, and a jack having an appropriate extension was placed on the floor in position to engage the bar. The jack was then raised to lift the bar, and thus the end of the conveyor roll, just enough to remove a shim from beneath the bearing housing journalling the end of the roll. The jack was then lowered which, of course, disengaged the worm wheel from the rotating worm on the line shaft, and the disconnected conveyor roll was removed from the conveying system of the lehr. Of course, a conveyor roll was installed in the conveying system by reversing the above-described procedure.
However, this procedure has not been entirely satisfactory in that damage to the drive train may occur because of the small amount of clearance provided between the worm wheel and the driving worm and the inability to precisely lift the bar and firmly hold the end of the conveyor roll with a floor supported jack. In accordance with the present invention, the movement of the end of the roll having a worm wheel can be precisely controlled and the end of the conveyor roll firmly held to prevent damage to the drive train while it is in operation.